Polymeric materials have previously been known which are effective for dispersing pigments in organic solvents. Such polymeric dispersants are typically of the AB or BAB types, in which a polar group known as the A segment is present in the molecule to facilitate attachment to a pigment surface, and at least one non-polar portion known as the B segment is present to enhance stearic stabilization of the pigment particles in a dispersion.
Baker et al, in U.S. Pat. No. 3,912,677, disclose the benefits of polymers containing ionic groups, in specific cases where the ionic groups are in the form of a salt with a salt-forming component or counterion. The salt-forming component has an affinity for the surface of organic pigment particles, and is capable of reaction with the polar-bound ionic group so as to form a salt. However, continued effort has been directed to improve the performance of polymeric dispersants, and to find effective dispersants that do not require the use of special salt-forming components, the use of which complicates the manufacture of the dispersants, and can introduce undesirable color.